To monitor and maintain the condition of technical systems in which fluids are involved as system components, it must be absolutely ensured that the fluids, for example, when they are used as lubricants, maintain the required performance characteristics in the course of operation. Thus, for example, in transmission oils routed through a cooler and a filter as they pass through systems of circulating lubrication, it is necessary to carry out testing of the filterability of the pertinent oils. Conventionally, for this purpose a sample amount of the oil is routed through a test filter, preferably such that a plurality of successive passages of the oil through the filter media is undertaken, that therefore a number of filtration cycles are carried out. This system also permits determination of the compatibilities between the given types of oil and the filter media. In addition, in this way filter passage and material compatibility between the oil and filter, especially with respect to additives, such as, for example, anti-foam and wear protection (EP/AW), can be tested. Furthermore, the effect of filtration on foam formation can be checked.
However, there is the danger that for oils provided with an anti-foam additive package which does not have sufficient stability in operation, after a longer filtration interval the concentration of the anti-foam additive decreases so that intensified, in some cases harmful, foaming of the oil occurs. Therefore it is necessary to check the oil for foaming behavior after a corresponding number of filtration cycles.